Orbiting telescope cooling off to find asteroids near Earth

Approved for an extended mission in August, NASA has reactivated the orbiting NEOWISE mission from hibernation, and the telescope’s infrared detectors are cooling off to undertake a renewed survey for asteroids coming perilously close to Earth, the project’s top scientist said Tuesday.

The electronic eyes inside the Wide-field Infrared Survey Explorer can only detect infrared light from cold asteroids when the detectors are chilled to frigid temperatures as low as minus 325 degrees Fahrenheit.

Amy Mainzer, principal investigator of the NEOWISE extended mission, said ground controllers have established communications with the WISE spacecraft. Engineers pointed the telescope away from Earth toward the cold darkness of deep space on Oct. 3, beginning a three-to-four-month chill down.

Since WISE was put in hibernation in 2011, the satellite was pointing its 16-inch telescope toward Earth for half of each 300-mile-high orbit, warming up the mission’s sensitive instrumentation.

“We’re now radiatively cooling,” Mainzer said Tuesday in a press conference at the American Astronomical Society’s 45th annual Division for Planetary Sciences meeting in Denver. “We expect to basically reverse this process.”

Mainzer said it would take several months to reach a stable operating temperature of about minus 325 degrees Fahrenheit, with science observations due to resume by the beginning of 2014.

NASA awarded the NEOWISE team $5 million annually over the next three years to scan the inner solar system for near-Earth objects, including rocks which pose a potential hazard to Earth.

“We’ll be discovering, we think, about 150 new objects over a three-year survey,” Mainzer said.

Most of the objects discovered by NEOWISE will be larger than the targets proposed for NASA’s asteroid retrieval mission concept, which calls for the launch of an unmanned probe to capture a small asteroid approximately 7 meters, or 23 feet, across and tug it back to a stable position near the moon.

Astronauts aboard an Orion spacecraft would blast off, perhaps as early as 2021, and rendezvous with the asteroid for research and spacewalks to gather samples.

Mainzer said the NEOWISE extension is not directly affiliated with the asteroid retrieval mission.

The WISE spacecraft was not tailored for asteroid hunting, and the modest rocks sought by NASA’s asteroid retrieval mission are tough to find, according to Mainzer, but it’s “quite likely” NEOWISE will find a few.

“These objects are very difficult to get at for a number of reasons,” Mainzer said. “For one thing, they’re just intrinsically very faint.”

The smallest rock spotted by NEOWISE three years ago was about 8 meters, or 26 feet, in diameter.

“It’s clear we have a lot of work to do to characterize the small end of the near-Earth object population,” Mainzer said.

Ground telescopes and future space-based missions may have a better chance of scouring the sky for small asteroids, Mainzer said.

“We are keen to find objects that are the most accessible because we think that would support a wide variety of missions,” Mainzer said.

NEOWISE’s infrared data will also yield key data on the size and reflectivity of many more objects, including asteroids already discovered by the telescope’s first round of observations in 2010 and 2011.

Mainzer said NEOWISE will look at a few thousand near-Earth objects over the three-year extended mission.

“It’s going to enable quite a lot of science,” Mainzer said, adding NEOWISE would also be observing nearby brown dwarfs and variable stars in two infrared wavelengths – 3.4 and 4.6 microns.

The mission will end in 2017 when the natural shifting of the satellite’s orbital plane around Earth puts the sun in the telescope’s field-of-view.

“By early 2017, we won’t be able to keep the sun out of the baffle effectively, and that’s going to end the mission,” Mainzer said.

WISE discovered more than 34,000 asteroids in the main belt between Mars and Jupiter, 135 near-Earth objects and 21 comets during its initial observing campaign in 2010 and 2011, according to a NASA press release.